1. Field of the Invention
The present invention relates to a time management scheme, and more particularly, a time management apparatus and a time management method for reducing the opportunity for a third party to intentionally tamper with time.
2. Description of the Related Art
Currently, a time stamp is employed for certifying the time in which a file for use has been made by using a computer and thereby ensuring security. Idealistically, it would be most preferable to provide this time stamp from an error-less clock maintained inside a computer or the like.
However, in reality, errors do occur in the clock provided inside a computer. Therefore, correction is required to be periodically performed by employing a clock serving as a criterion. One example as a clock serving as the criterion for correction is a radio-wave clock.
With a conventional technology, in a case where external time information, which is transmitted by radio wave from a radio-wave clock, is receivable by a time management apparatus, the time management apparatus calibrates using the transmitted external time information. On the other hand, in a case where the external time information cannot be received, time information from a built-in local clock is used without performing calibration.
In this case, however, there is a problem that public time information transmitted from the radio-wave clock cannot be used as a digital signature time stamp since there is a possibility that the time indicated by the local clock is freely tampered by using a false radio-wave clock transmitter.
Furthermore, with a conventional technology, in a case where the local time indicated by the time management apparatus is earlier than an external time provided from outside, the time output from the time management apparatus slightly returns to a time of the past when the external time from outside is fetched into the time management apparatus. In such a case, the time stamp of the time period indicated by the time of the past loses credibility.
Furthermore, a method of certifying the validity of the time of a time stamp is desired.
Furthermore, the documents below describe technology related to the present invention: Japanese Laid-Open Patent Application Nos. 6-258460, 2003-4876, 2002-236187, 2002-63614, 2002-185449, 2003-218860, and 2003-524348.